1. Field of the Invention
The present invention relates to an imaging apparatus, a control method of an imaging apparatus, and a computer program. More specifically, the invention relates to an imaging apparatus, a control method of an imaging apparatus, and a computer program, which allow a quick, accurate Auto focusing process for a target subject.
2. Description of the Related Art
Many imaging apparatus nowadays such as a still camera and a video camera have an auto focusing (AF) mechanism mounted thereon which automatically bring a subject into focus. In addition, in recent years, in a camera having an auto focusing (AF) function, such a function, a so-called “Multi AF”, or “multipoint range AF”, is widely adopted, which measures a distance to a plurality of areas in a screen, selects the optimum area resulting from various priorities such as one being closest to a photographer, and one being closer to the center of the screen, and drives a lens to bring the area into focus. This function is applied to allow proper focusing for a main subject with no special operations done by a photographer even though the main subject is not always on the center of the screen. Moreover, for the configuration of auto focusing control, for example, it is described in Patent Reference 1 (see JP-A-4-000421).
However, such the Multi AF or multipoint range AF function does not serve for all purposes, and these functions are effective only for a specific composition. In general camera shooting, people are a main subject in a great many cases, but people are at many places in a taken image, and there are various compositions. In the first place, in some cases, a target subject is at the position at which the area to measure a distance is not set in an imaging apparatus. In this case, even though the Multi AF or multipoint range AF function is applied, people are not brought into focus properly.
In order to solve such problems, such a configuration is proposed in which a face is recognized from an image in an imaging apparatus, and the area to measure a distance is set at the position of the recognized face that, whereby the face can be brought into focus in any compositions. For example, Patent Reference 2 discloses a configuration of focus control based on such face recognition (see JP-A-2003-107335). By the focus control based on this face recognition, proper focus control (focusing) is allowed in shooting various compositions.
However, in order not to lose a chance to take a picture, time consuming processing is not suited. In other words, the AF function that merely brings the face into focus in the area to measure a distance is not enough, and it is necessary to contrive a scheme for accelerating the AF function. For the configuration which proposes focus control processing in the point of view that focus control is done quickly and a chance to take a picture is not lost, for example, there is Patent Reference 3 (see JP-A-60-254207). In Patent Reference 3, an apparatus is proposed in which a particular subject is recognized to measure a distance while the subject is being kept track, and focus control is quickly performed to allow shooting that will not lose a chance to take a picture.
However, in such an AF function which keeps track of a main subject, a problem is: what is a main subject for a photographer? For one of schemes of solving this problem, it can be considered that there is a scheme in which a face is recognized from an image to determine whether the face is a main subject or not. However, in this scheme, in a scene in which there is a plurality of people, it becomes a problem which person should be set to a main subject.
As described above, the auto focusing (AF) function has various problems to be solved, but for a basic function that is demanded to implement ideal auto focusing (AF), it can be considered that three points below are most critical.    1. To ensure that a main subject is brought into focus.    2. To obtain focus for a short time.    3. To ensure that a subject to be brought into focus is quickly selected among a plurality of possible main subjects.
Furthermore, another basic demand is to reduce costs. It is not preferable to increase costs for implementing the function. For example, such a configuration is desirable that reliably implements quick focus control with no use of an external distance measuring apparatus such as an expensive range sensor.